Allen Park — Bill Belichick’s coaching tree has always been a thorny subject in the NFL.

The failures of his former assistants out on their own are well-documented, each of them seemingly tripped up by their own arrogance or abrasiveness, and to be fair, the absence of a franchise quarterback.

So it should surprise absolutely no one — least of all the players in Detroit — that Matt Patricia’s early days here haven’t been all that rosy.

This was part of the deal when Lions general manager Bob Quinn brought in his coaching pal from New England, the smart guy with the beard and the pencil and the Patriots pedigree, not to mention a five-year contract and a mandate to get tough — or get going.

More than 40 percent of the Lions’ roster has turned over since last season, and that’ll continue apace in the coming months. But for the players who stuck around — those who were here before under Jim Caldwell — the system shock was inevitable.

“The players that were here previously, I’m pretty sure a lot of us are, like, ‘Yeah, this is tougher, this is different, it’s this or it’s that,’” veteran safety Glover Quin said. “But that’s always expected when you have a new coach.

“Their personalities are completely different. So obviously the way things are brought about are completely different. It’s just the way it is. And if that’s all you know, that’s all you know. So it happens, every team, and you just deal with it. Your job is to go out and play football.”

No issues

Do your job. That’s the well-worn mantra in New England, and the one Patricia’s trying to imprint on a new team now that he’s here, whether it’s in the defensive scheme on the field or the stricter rules around the practice facility.

The ping-pong tables are gone, and so are the shorter practices. But so is the bond that Caldwell had built over the last four years with his players, and the trust that came with it. And it’s going to take more than simply time on task for Patricia to forge anything like it in his first go-around as a head coach.

If New England really is the blueprint they’re using here, it’s going to take winning, and maybe nothing else, which is why the reports of grumbling players and general discontent in Allen Park shouldn’t be ignored, nor should they be exaggerated at this point.

And Patricia, for his part, isn’t buying the concerns about his players buying in, saying, “I don’t see any issues there whatsoever.”

Matthew Stafford also offered an endorsement of sorts, for what that’s worth.

“He’s just a fiery, competitive, aggressive guy that is going to do everything he can to help us try and be successful,” Stafford said, when asked about Patricia’s coaching style. “And that’s a great thing to have.

“I mean for me, I appreciate it. I understand that we’re doing everything we can to try and win. And you can’t let any kind of message get lost in the delivery of anything.”

When you see that play out, it’s hard not to wonder how it’s being viewed from within.

“There’s a lot of guys in the locker room,” Quin said. “There’s no way that everybody is gonna be completely happy. … There’s always complaints. That’s just part of human nature.”

So is this: Nothing fuels dissent quite like losing does. So the immediate danger here — if not for Patricia, at least for the Lions’ 2018 outlook — is that the results don’t come soon.

Quin downplayed that suggestion Wednesday, and understandably so. He’s a 10-year vet who is playing for his fourth head coach and fifth defensive coordinator. He’s seen a little bit of everything in his career.

Still, like most of the veteran holdovers on this roster, he respected — and appreciated — Patricia’s predecessor for reasons other than the obvious ones, and in ways fans probably wouldn’t understand.

So he knows where this line of questioning is coming from, too.

“I guess everything is better when you’re winning,” Quin said. “It’s hard to complain when you’re winning. You’re winning, so whatever you’re doing must be working, right? … When you lose, a lot of stuff comes out. When you win, nothing comes out. It’s just the nature of the beast.”

But it’s a beast the Lions’ new boss better get tamed before it does too much damage.